The mining, construction and other industries, are increasingly employing automation and robotics to enhance the efficiency of material processing operations, such as excavation and mining activities, using powered equipment, often with articulated arms having independent joint connections between the links. Some machines have built-in mechanical means to coordinate joint motions.
Many tasks require a human operator to coordinate the movement of several machine links by simultaneous control of a corresponding number of joysticks or other control devices. One example is the control of earth moving equipment such as an excavator employing a bucket as a tool. It can be a difficult, skilled task, often requiring years of experience effectively to control the machine so as to move the tool along a desired path with an efficient trajectory. The task demands continuous concentration and careful adjustment by the operator of multiple links so as to effectively control their motion.
Roberts, J. M. & Corke, P. I. 1997. in “Automation of underground truck haulage.” Fourth International Symposium on Mine Mechanization and Automation have described automated load-dump haulage roadheaders. Kogler, P., Melrose, R., Stratmann, T. & Sifferlinger, N. A. 1997. “Further approaches in automation on roadheaders/bolter miners in production and development.” Fourth International Symposium on Mine Mechanization and Automation: A6-11-A6-18. have described partially automated dragline stripping, production drilling, rock bolting, and shotcreting.
Of particular exemplary, but non-exclusive, interest for automation are large mining front end shovels. Such excavating machines may perform several hundred shovel cycles per day, each cycle including filling the machine's bucket, hoisting and swinging the load over a haul truck, dumping the load, and returning to the digging front. The term “bucket” is often used generically in the art to include a “shovel” and other tools with which an excavator arm may be equipped. Stentz, A., Bares, J., Singh, S. & Rowe, P. 1999. in A robotic excavator for autonomous truck loading. Autonomous Robots 7: 175-186. have proposed using sensory adjustments to vary the digging and loading points with a view to rendering fully robotic the repetitive components of the operations of a front end shovel. To integrate such fully automated or robotic components into the complex operations performed by mining and construction equipment, may require human supervisory control.
Employment of a human operator, even in a supervisory capacity, is contrary to traditional industrial robotics practice, for example for assembly and paint spraying operations and the like in automobile manufacture, where the absence of a real-time human supervisor is an important advantage of robots. Unlike the “cookie cutter” complex but repeated operations common in manufacturing robotics the flexibility and diversity of operations required in mining, construction and the like may justify or require the partial or even full-time attention of a human operator even when an automated machine is utilized. In general, robotics systems are designed to perform large numbers of iterations of a procedure or suite of procedures or selection of one or more procedures from an available suite, each of which procedures or suite of procedures is familiar to the robotic system. In contrast, an ability to adapt to unfamiliar terrain, environment or circumstances is a prerequisite of mining and construction operations. For these reasons alone, known robotics methods may not be suitable for automation of mining and construction equipment and the like.
Furthermore, conventional robotic equipment is generally unsuited to a mining and construction environment. Industrial robots employ precision engineering with fine-tuned valves and mechanical controls and sensitive hydraulics that require scrupulously clean oil. In a typical modern factory having a climate- and dust-controlled, indoor environment, these conditions can usually be met without undue difficulty. A typical mining or construction site offers quite the opposite conditions, presenting a hostile environment to industrial robotics. The air is typically dust and dirt laden. The equipment, as robust as it is, operates to relatively crude tolerances and commonly functions satisfactorily under mining conditions. Accordingly, severe problems may be encountered in adapting the principles of industrial robotics for operation of mining or construction machinery or the like.
Perreira et al disclose in U.S. Pat. No. 4,763,276 a robot control method intended to locate a robot at a desired position and orientation (pose) wherein an anticipated pose of a robot is predicted, compared with a desired pose and a correcting command signal is employed to place the robot.
Chan et al disclose in U.S. Pat. No. 4,893,254 a manipulator arm position sensing method wherein smoother operation of an the movement of the end point of an articulated arm to a preselected target is obtained by computer calculation of joint angle changes using an iterative pseudo inverse Jacobian having a damping factor. Though presumed to be useful for their intended purposes, neither the Perreira et al. nor the Chan et al. methods is suitable for controlling excavation or construction machinery in a manner capable of automating repeated operations and permitting flexible machine operation in a changing or diverse environment.
As shown in FIG. 1, Alami, R., Chatila, R., Fleury, S., Ghallab, M. & Ingrand, F. 1998. in “An architecture for autonomy.” The International Journal of Robotics Research 17(4): 315-337. have proposed a control architecture for mobile robots which reportedly integrates human supervisory direction into an automated robotic machine. Referring to FIG. 1, a human supervisor 10 observes the motion and position of an end effector 12, and provides mission guidance, to a trajectory planner 14. Trajectory planner 14 selects a software control protocol corresponding with the mission guidance instruction and provides power and motion control to the machine actuators, for example hydraulic pistons and cylinders to execute the mission guidance instruction. The trajectory is planned either in Cartesian or joint space. The software control protocol iterates every step needed, including every actuator adjustment, for the end effector to execute the desired trajectory.
The term “end effector” is used in the context of the invention herein, to reference the ultimate point or object component of the machine or system that is manipulated by the machine or system, for example a tool such as a front end loader shovel or drill, or an object picture in an imaging device.
An example of such an integrated, human controlled partially robotic operation is that of a three-boom robotic tunneling drilling machine each boom of which collars, corrects the alignment and drills a hole. Ideally, a supervisor, who is effectively a robotic operator, “manually” checks and corrects the collaring of each pre-programmed drill hole using the machine's joysticks or other manual controls, but employs built-in automation to complete the drilling of each hole. If effective, the collaring and manual correction of the alignment and determination of the coordinates of the next hole can be made while the two other booms are drilling automatically. This is a typical example of sequentially applying operator adjustment and robotic automated control of a predetermined trajectory element.
One known, robot control scheme suitable for control of a joint-based, continuous-path end effector is illustrated in FIG. 2. Referring to FIG. 2, the control scheme shown employs a Cartesian trajectory generator 16 and the control architecture allows the motion to be executed at a desired speed and the actual movement to be adjusted relative to the basic trajectory. For this control scheme, the desired trajectory is assumed to be predefined, either as a preprogrammed or as a user-recorded pattern.
Operation of one of the levers or controls 16 of the excavator's manual control unit 18 provides a Cartesian position control signal to a trajectory generator 20. Trajectory generator 20 utilizes a time division base 22 to generate control signals comprising desired joint position, velocity and acceleration signals for moving a particular machine link through a desired trajectory. Trajectory generator 20 employs forward kinematics, using a model to determine where the end effector should be at a future point in time. The control signals are supplied to a joint control system 24 which provides an appropriate power signal to robot actuators 26. Real-time integration of the operation of any or all levers 16 in each of three Cartesian directions yields machine kinematic configuration and an output which determines the actual Cartesian end effector position 30 over time. Feedback control is provided by position sensors (not shown) at the robot actuators which provide joint position and velocity signals to the joint control system 24 enabling internal position error correction.
Mathematically, the three-dimensional trajectory of the end effector can be described by employing a surrogate variable for the definition of the trajectory as functions of three Cartesian position control signals, without specifying velocity. The motion velocity can be given as the tangential velocity along the path. The incremental arc length of the path can be related to the partial displacements in the three Cartesian directions to provide the relationship between time and the surrogate variable for a given motion. This relationship may be assumed to be solved by using an appropriate initial condition for the motion. Further simplification can be obtained for the special case where the selected parameter is identical with the arc length of the path. In this case, the variation of the surrogate parameter over time can readily be determined.
Variations in the tool orientation may be described by defining the tool direction with an ordered set of absolute-angle or Euler-angle rotations, one for each degree-of-freedom of the automated robotic machine, in a comparable manner to the description of the translational motions and displacements using a surrogate parameter. If the variation of the parameter with time is based on the position definition, the angular velocities can be defined and no further velocity relationship is needed. Otherwise, a further equation is required to specify the angular velocity, for example by prescribing the rate of the equivalent angular rotation as a function of the surrogate parameter. The position and angular velocities can then be defined in real time. For further purposes, the angular velocities of the ordered rotations with time can be determined based on the foregoing approach, using manipulator kinematics formulations, such as described e.g., by Craig, J. J. (1989) “Introduction to robotics: mechanics and control.” 2nd Ed. Addison-Wesley, Reading, Mass.
This conventional control system is suitable for continuous path robotic control and in effect models the desired trajectory of the end effector in system space and applies power signals to the machine actuators of an amplitude and duration calculated to achieve the desired trajectory in real space. However, it is deterministic, the end effector can only travel on a preprogrammed path, the control does not permit human supervisory participation, and cannot adapt to new circumstances, such as novel changes in the end effector working environment.
A completely manual control based only on a human operator is shown in FIG. 3 for comparison, as another conventional system. Danko, the inventor herein, in “Coordinated Motion Control.” Presentation to Sandwick-Tamrock Personnel, Tampere, Finland in 2000 (“Danko 2000a” hereinafter) described a modification of the conventional robot control scheme shown in FIG. 2, for human supervisory control, which modification is schematically illustrated in FIG. 3. In this example, in order to show for comparison the complexity of prior art approaches, human supervisory control of the end effector position and orientation is accomplished by adjusting the motion velocity components of the joint or machine actuators and integrating the individual components with respect to time much as is done in the manual supervisory control scheme illustrated in FIG. 1. The main component of the motion control is the manual guidance of the tangential and angular velocities along the pre-determined path. Other control inputs can be used to modify the trajectory. Translational and rotational trajectory modifications can be accomplished by adding position correction terms to the absolute position. The solution example, however, requires the combination of ordinary robotic control with a supervisory adjustment which further increases the inherent complexity of a robotic system.
The foregoing description of background art may include insights, discoveries, understandings or disclosures, or associations together of disclosures, that were not known to the relevant art prior to the present invention but which were provided by the invention. Some such contributions of the invention may have been specifically pointed out herein, whereas other such contributions of the invention will be apparent from their context.